A general election for the Japanese House of Representatives was held on August 30, 2009. The opposition Democratic Party (DPJ) defeated the ruling coalition (Liberal Democratic Party (LDP) and New Komeito Party) in a sweeping victory, winning 221 of the 300 electoral districts and receiving 42.4% of the proportional block votes for another 87 seats, a total of 308 seats to only 119 for the LDP (64 districts and 26.7% of the proportional votes).[1][2][3]

The 2009 election was the first time since World War II that voters mandated a change in control of the government to an opposition political party.[6] It marked the worst defeat for a governing party in modern Japanese history, was only the second time the LDP lost a general election since its formation in 1955, and was the first time that the LDP lost its status as the largest party in the lower house; the only other break in LDP control since 1955 had been for a 3-year period from 1993 to 1996 (first 11 months in opposition, then participating in a coalition government under a Socialist prime minister).[7]

The last general election took place in 2005 in which the LDP, led by popular prime minister Junichiro Koizumi, received 38.2% of the proportional block votes and 47.8% of the district votes cast (the next largest party, the DPJ, received 31% in the proportional and 36.4% in the district vote). Due to the characteristics of the Japanese election system, the LDP ended up with 296 seats in the Lower House (61.6%), which enabled Koizumi to complete the privatization of Japan Post. Since then Japan has had three further prime ministers (Shinzō Abe, Yasuo Fukuda and Taro Aso) who have come to power without there being a general election.

On September 1, 2008, Yasuo Fukuda abruptly announced he was retiring as leader. Taro Aso won the subsequent LDP leadership election, which was held on September 22, 2008.[8] Media sources speculated that, in the wake of a recent change in leadership, Prime Minister Taro Aso might call elections in late October or early November 2008 while his popularity was still high,[9]

There were expectations that the steady decline and numerous scandals of the LDP might lead to the complete extinction of the party and the creation of a new political system, with actual ideologically coherent parties emerging instead of the current system of a shared interest in power with stark ideological differences.[10]

In late June 2009, there were rumours of a planned election date in early August 2009.[11] In prefectural elections in Tokyo, the LDP again lost a lot of seats and was for the first time since 1965 not the largest party in the prefectural assembly. The next day, Aso confirmed these rumours by calling for an election on August 30, 2009.[12]

As soon as the election was called, a campaign was underway by a group of LDP Diet Members to replace Aso as leader. Fully one-third of the parliamentary party (including finance minister Kaoru Yosano) were reported to have signed a petition calling for an urgent party meeting to discuss the issue. The BBC reported LDP critics of Aso asserting that an election with him still as leader would be "political suicide".[13] Prime Minister Aso dissolved the House of Representatives on July 21, 2009.[14] The official campaign started on August 18, 2009.[15]

The DPJ's policy platforms include: a restructuring of civil service; a monthly allowance for families with children (at 26000 yen per child); a cut in the fuel tax; income support for farmers; free tuition for public high schools; the banning of temporary work in manufacturing;[17] raising the minimum wage to 1000 yen; and the halting of any increase in sales tax for the next four years.[15][18][19]

The LDP's policy platforms are similar to the DPJ's. A New York Times article on August 28, 2009 noted both platforms offer little on economic policies.[20]

Before the dissolution of the lower house, National weekly magazines had been citing analysts predicting a big loss for the ruling coalition which held two-thirds of the seats in the House of Representatives. Some (e.g., Shūkan Gendai[21]) warned that the LDP could lose as much as half of that. Many based their predictions on the low approval rating of the Prime Minister Taro Aso and the devastating loss that the LDP suffered in the earlier prefectural election in Tokyo. On August 20 and 21, 2009, Asahi Shimbun and Yomiuri Shimbun, leading national newspapers, and Nikkei Shimbun, a financial daily, reported that the DPJ was poised to win over 300 of the 480 contested seats.[22][23][24]

On August 22, 2009, Mainichi Shimbun went further to predict that the DPJ could win over 320 seats, meaning almost all DPJ candidates would win.[25] Mainichi noted that the DPJ appeared to be doing well in the western part of Japan, a traditional stronghold of the LDP, and that the LDP could lose all of its single-member constituency seats in 15 prefectures, including Hokkaidō, Aichi, and Saitama.[26] Also, according to Mainichi, the Japanese Communist Party will probably retain its previous 9 seats, while the Komeito Party and the Social Democratic Party may lose some of their shares.

According to a poll conducted on August 22, 2009 by the Yomiuri Shimbun, Japan's largest newspaper, 40 percent said they would vote for the DPJ, while 24 percent for the LDP.[27]

The DPJ swept the LDP from power in a massive landslide, winning 308 seats (out of a total of 480 seats), while the LDP won only 119 seats[1] - the worst defeat for a sitting government in modern Japanese history. This was in marked contrast to the 1993 election, the only other time the LDP has lost an election. In that election, the LDP remained by far the largest party in the House with well over 200 seats, despite losing its majority. However, in the 2009 election the LDP was nearly 200 seats behind the DPJ. Of 83 Koizumi Children who became new LDP representatives in 2005, only 10 were reelected.

The DPJ won a strong majority in the House of Representatives, thus virtually assuring that Hatoyama would be the next prime minister. Under the Constitution, if the House of Representatives and the House of Councilors cannot agree on a choice for prime minister, the choice of the House of Representatives is deemed to be that of the Diet. Hatoyama was nominated as prime minister on September 16 and formally appointed later that day by Emperor Akihito.

However, the DPJ was just short of a majority in the House of Councillors, and fell just short of the 320 seats (a two-thirds majority) needed to override negative votes in the upper chamber. Hatoyama was thus forced to form a coalition government with the Social Democratic Party and People's New Party.[30]

Had the parties nominated a sufficient number of candidates on their proportional "block" lists, the election result would have given the DPJ two additional seats in Kinki, the YP one in Kinki and one in Tōkai. In Kinki, two seats went to the LDP, one to Kōmeitō, in Tōkai one to the DPJ.[40] For the same reason, one Democratic Kinki proportional seat fallen vacant in 2010 (Mitsue Kawakami) cannot be filled until the next general election.

In March 2011, the Supreme Court decided that the malapportionment of electoral districts in the 2009 election had been in an unconstitutional state. As in previous such rulings (elections of 1972, 1980, 1983 and 1990), the election result is not invalidated, but the vote weight disparity must be reduced by the National Diet soon. The 2009 election has been the first House of Representatives election ruled unconstitutional since the electoral reform of the 1990s and the introduction of parallel voting in single-member districts and proportional "blocks".[41] The two major parties want to use the reform to also significantly reduce the number of proportional seats as both had promised in their 2009 campaigns, but meet resistance from the smaller parties that depend on proportional seats.[42][43]